I'm having the same issue, but usually not only with RPG's. Just mod single player (story) games. For some reason I keep going back to the few games I like and they're all sandbox (Dota 2, ETS2, Cities: Skylines).
Whenever I start an RPG I'll have to see if I like it first, then I decide that I want to finish it and I don't. I had to restart the witcher 3 times because I forgot all the controls and needed the tutorial to relearn them. But that kind of burns me out of the game because I already know the first 2 hours of the story so it gets boring. I just have to force myself to continue with the game. It's not that I dislike doing that, but if I don't the game just sticks in my library for months or years without me touching it again.
I played DA:O for about 30 hours and enjoyed it alot. For some reason I stopped playing and now I just can't be bothered to either continue or restart.
There's actually a plus side from Skyrim with the Alternative Start mod, you can restart the game without having to go through that annoying intro video everytime you start a new game.
It took me 4 years to finish GTA5, which I think is not an RPG but yet, I found it hard to finish. Could it be that those games just tend to be too long? Even when interesting, 180 hours for a game is alot of time. Tomb Raider games I finished in 15-30 hours each, which seems a pretty good timing for me. Let's me finish a game after about 2 weeks of playing and after 2 weeks what happened on day 1 can be pretty fresh in your mind.
Another issue for me might be that I tend to try too many games at the same time so I might end up messing up controls. When playing Skyrim and Oblivion, they both have very different controls for the same actions.